Q: When I removed dark polish from my toenails, I noticed that they had turned partly white. What causes this and is it harmful?

A: Yikes. I hate these kinds of surprises, which seem to happen more often the older I get. I'm afraid one morning when I get up and go to look in the bathroom mirror, one of my eyeballs is just going to drop out and fall in the sink. But back to your unpleasant surprise. If your entire nail is white (not yellow, which is simply a stain from the dark polish), you should see a dermatologist, who can determine whether you have a fungal infection; there is a rare type that looks like a chalky white coating of the nail, says Robyn Gmyrek, MD, assistant clinical professor of dermatology at Columbia University. But if you have white marks on your nails, they're most likely a result of trauma to the nail bed, which you probably got when you or a pedicurist pushed back your cuticles. The cuticle protects the matrix, the part of the nail responsible for creating the nail plate (the hard part you can see); when cells in the matrix are injured, they grow out white. Gmyrek says she sees lots of patients concerned about horizontal, ill-defined whitish lines on their toenails, and she encourages them to make sure they or their pedicurist uses an orange stick for pushing back cuticles, rather than a metal instrument, which is more likely to damage the nail bed.

Bottom line: Take extra care when pushing back your cuticles; any white areas on your nails will grow out completely in 12 to 18 months.